Nodal spring assembly for an electronic toothbrush

ABSTRACT

A nodal-mounted spring arrangement for an electronic toothbrush includes a V-shaped spring member secured at both ends so that it can operate in out-of-phase torsion mode along the axial dimension thereof. In one embodiment, the V-shaped spring member includes two extended end regions, which extend below a longitudinal edge of the middle portion of the V-spring. The free ends of the extended portions are joined by a flat cross-piece. This “closed end” region is present at both ends of the V-spring.

This invention relates generally to drive train assemblies for anelectronic toothbrush, and more specifically concerns a nodal springarrangement for such a drive train.

Various drive train arrangements are known for electronic toothbrushes.The drive train portion of the toothbrush is responsive to a motoraction, including mechanical, electromechanical, magnetic or otheraction, to drive a brushhead in a reciprocating manner. One type ofdrive train arrangement uses a spring which is fixedly mounted at bothends as well as at a node point, wherein the node point is between thetwo ends of the spring, typically mid-length. When the drive actionexcites the spring in its desired out-of-phase torsion mode, it producesa desired reciprocating brushhead action through a selected angle.

In one arrangement, the nodally mounted torsion spring is V-shaped,having a node point which is connected to the housing by a mountingplate. In such arrangements, the mounting plate, which acts as a groundconnection for the V-shaped torsion spring bar, is connected to thehandle frame/housing, reducing vibrations which would otherwise betransferred to the handle. The V-shaped torsion bar, which acts as anode spring, has several important functions, including returning thebrushhead, or other workpiece, to a center position and to clearlyseparate the in-phase rotational mode from the desired out-of-phaserotational mode sufficiently to avoid interaction between the two modes.Such a V-spring arrangement is described in U.S. Pat. No. 6,859,986, thecontents of which are hereby incorporated by reference. That patent isowned by the assignee of the present invention.

In the above-described nodal spring arrangement, there are severalstructural challenges to achieving a desired and reliable operation. Itis important that the node spring be arranged so that the desireddynamic response of the torsion spring is achieved and to reduce thehigh stresses and the potential for wear in the area of contact betweenthe V-spring and the mounting plate. It is also important that theresponse of the V-spring be as linear as possible along the lengththereof, as opposed to a non-linear response.

Accordingly, the present invention is a spring assembly for a drivetrain used in an electronic toothbrush, comprising: a V-shaped springmember which is secured at both ends so that it can be excited in atorsion mode about a node point along the axial dimension of theV-shaped spring member; an insert member for closely supporting a lowersurface portion of the V-shaped spring member; a shim member positionedbetween the V-shaped spring member and a node spring member which isconnected to the housing of the toothbrush; and an attachment member forsecuring the node spring member, the shim, the V-shaped spring memberand the insert tightly together.

FIG. 1 is a perspective view of a portion of an electronic toothbrushshowing a V-spring with an integrated node spring function and mountingplate drive train arrangement for an electronic toothbrush.

FIG. 2 is a perspective view showing the V-spring portion of thearrangement of FIG. 1 in more detail.

FIG. 3 is an exploded view showing another V-spring and node springarrangement in an electronic toothbrush.

FIG. 4 is a cross-section view showing one variation of the embodimentof FIG. 3 in more detail.

FIG. 5 is a perspective view showing a portion of the variation of FIG.4 in detail.

FIGS. 6A and 6B show another portion of the variation of FIG. 4.

FIG. 7 is an elevational view of another variation of the embodiment ofFIG. 3.

FIGS. 8A and 8B are perspective views of portions of the variation ofFIG. 7A and 7B.

Referring now to FIGS. 1 and 2, a nodal drive train assembly portion ofan electronic toothbrush is shown which incorporates one embodiment ofthe nodal mount assembly disclosed herein. The nodal drive trainassembly shown at 10 includes a front end portion 14 of anelectromagnetic motor, driving a V-configured torsional bar spring 15.The remainder of the motor is in a handle portion of the toothbrush (notshown). Such an electromagnetic motor arrangement is disclosed in U.S.Pat. No. 5,378,153, which is owned by the assignee of the presentinvention, the contents of which are hereby incorporated by reference.At the other end of drive train 10 is a portion of a toothbrush headassembly 16. In one arrangement, the entire drive train assembly,including the head assembly, is removable from a handle portion of thetoothbrush and replaceable as a unit, while in another arrangement, abrushhead is removable by itself from a mounting member at the distalend 17 of drive train 10.

The V-shaped solid torsion member 15, also referred to as a torsionspring, extends between the two portions 14 and 16 and is fixedlysupported by two end mount assemblies 20 and 22, which can be of variousconfigurations. In a particular embodiment, the torsion member 15 isapproximately 35 mm long, and comprises two identical plate portions 21and 23, which are approximately 4.25 mm wide and 0.30 mm thick, madefrom spring steel. The assembly shown in FIG. 1 is typically supportedto the housing of the toothbrush by spaced bearing assemblies (notshown) at the opposing ends thereof. A detailed example of such anarrangement of a nodal mounted drive train is shown and described in the'986 patent.

In operation, the drive motor action excites the torsion bar spring 15in its out-of-phase mode, such that rotation of the proximal half 27 ofthe torsion spring in one direction results in a rotation of the distalhalf 29 in the opposite direction. The frequency of the out-of-phasemode is approximately 270 Hz in the embodiment shown.

In this embodiment, a mounting plate 26 is fixedly connected to the nodepoint 30 of the V-shaped torsion spring by welding or similar fixedconnection. The node point is located approximately midway of theV-shaped member, along the ridge line 31 of the V-shaped member. Themounting plate is also connected fixedly to the housing of thetoothbrush. This arrangement reduces the vibration of the handle.

In the embodiment of FIGS. 1-2, the stresses typically present at thenode joint are reduced by a pair of slots in the V-shaped member. Theslots, which result in the V-shaped torsion spring member functioning asa torsion bar node spring, 32 and 34 in the embodiment shown, aresubstantially identical and are located close to the ridge line, onopposite sides of the node point 28 in the respective plate portions 21,of the V-shaped bar member. The slots 32, 34 extend longitudinally ofthe V-shaped member and are approximately 8 mm long and 2.4 mm wide. Theeffect of the slots is to more evenly distribute the stresses along theV-shaped member and reduce the stress in the vicinity of the node point28, as well as integrating a node spring function into a torsion bar 15.The slots, while generally being uniform in width along their length,may include small tab portions which decrease the slot width at thosepoints.

FIGS. 3-7 show another embodiment of the present invention. FIG. 3 showsa nodal drive train arrangement 40 which includes a V-shaped bar springmember 50 which is fixedly mounted at the respective ends thereof to endmount assembles 42 and 44. End mount assembly 42 is driven by a motor(not shown);

extending from end mount 44 is a mount 48 for a brushhead assembly. Aswith the first embodiment, the entire drive train can be madereplaceable relative to a handle portion of a toothbrush, or thestructure can be arranged so that the brushhead assembly alone isreplaceable.

V-shaped bar spring member 50, shown in FIG. 3 includes two extended endregions 501 and 502, which extend below the longitudinal edges 503 ofthe middle portion of the V-spring. The width of the end regions is wideenough to accommodate the size and configuration of the portion of theend attachment assemblies which contact the spring. The free ends of theextended portions are joined by a flat cross-piece 504. This “closedend” region is present at both ends of the V-spring. Preferably, thecross-piece 504 is integral, i.e. unitary, with the remainder of thespring, with the ends of the extended regions of the spring and thecross-piece having curved joints 505 for a smooth transition, referredto as closed end regions. The cross-piece could also, however, be aseparate piece of material, attached by welding or other means, for someapplications. The V-spring includes three openings along the peak of theV-spring one at either end to accommodate bolts for clamping theV-spring in a particular assembly and another at the center toaccommodate a bolt for a nodal attachment member.

Extending between support members 42 a, 44 a, which are mounted in endmount assemblies 42, 44, is a V-shaped torsion member 50, whichfunctions as a spring. Mounted to the center point (node point) 48 oftorsion spring 50 is a separate node spring 52, in the form of amounting plate, unlike the embodiment of FIGS. 1 and 2 in which thenodal spring function is integrated into the V-shaped bar member. Themounting plate (node spring) 52 is fixedly attached to the housing ofthe toothbrush at its outer edges thereof. In this arrangement, mountingplate 52 is secured to the V-shaped torsion spring 50 (V-spring) by amounting assembly, which includes generally a base insert member 54which fits within the trough portion 56 of the V-shaped torsion spring50, a shim member 57 which is positioned between the torsion spring 50and the node spring 52, configured to provide a stable connectiontherebetween, and an attachment member combination 58, 59 which securesthe entire assembly firmly together.

There can be several structural variations of the general arrangementshown in FIG. 3. In all of the variations, however, there are severalcommon functions of the assembly. First, the axis of rotation of thenode spring (i.e. mounting plate) 52 should be as close as possible tothe axis of rotation of the V-spring 50, in order to achieve the desireddynamic response. Second, the mounting assembly, specifically theinsert, shim and the attachment member combination, must provide astable, strong connection between the V-shaped torsion spring and thenode spring (mounting plate) at the node point, in such a manner as towithstand the particular stress at the node point connection for anextended period of time, while also reducing the stresses at that point.Third, the joint must be strong and fixed, so that the out-of-phaseresponse of the V-shaped torsion spring is as linear as possible.

In a first variation, shown in FIGS. 4, 5 and 6A, 6B, the insert member62 is a diamond-shaped assembly. Referring to FIGS. 4 and 5, shoulder(side) portions 64 are flat, configured generally to provide a goodextended clamping surface between the insert 62 and the V-spring 63. Theedges 64 a of the insert round downwardly to avoid stressconcentrations. The curve of the upper surface portions 66, 67 is suchas to correctly mate the insert relative to the inner surface of theV-spring where the two plate portions thereof meet. The upper surfaceportions of the insert must have a slightly larger radius than thecorresponding internal surface area 68 of the V-shaped torsion spring sothat the torsion spring will sit flush on the flat shoulder portions 64when the assembly is clamped together. An opening 69 extends through theinsert member 62 for the attachment member.

A first shim member 56 for the first variation is shown in FIGS. 6A and6B. Referring to FIG. 3, shim member 56 is in the general form of aV-shaped block and is configured to fit on the top surface of theV-shaped torsion spring 50, providing a stable clamping surface for thenode spring 52. Flat side shoulder portions 70, 71 provide a clampingsurface to the

V-spring 50, while surface portions 72, 73 mate with the correspondingjoint area (the upper surface of the bend) between the two plateportions of the V-spring 63 (FIG. 4). Outer edges 74 and 76 of surfaces70-73 of the shim curve outwardly, avoiding the stress concentrations.Surface portions 72, 73 have a smaller radius than the radius of themating surfaces of the V-spring, so that the V-spring will contact flushthe flat shoulder surface portions 70, 71 of the shim. An opening 80through the shim is provided for the attachment member.

The opposing side of the V-block shim 56 includes a raised surfaceportion 82 which provides a keying function for positioning of the nodespring (mounting plate) 81 thereon, while an adjacent flat surface 84portion provides a clamping surface between node spring 81 and shim 56.The raised surface 82 extends into a mating opening in the node spring81. The keying function can be accomplished by many different surfaceconfigurations, as long as the structure can react the torque loads onthe joint.

Both the diamond-shaped insert and the V-block shim are shaped generallyto allow the V-spring to deform in a manner as close to its naturalstate as possible, and to minimize stress increases, while at the sametime providing substantial clamping surfaces between the assemblyelements. The shim aligns the V-spring to the node spring and sets thegap between the node spring and the V-spring to prevent rubbing movementduring operation.

The entire assembly (FIG. 3) is clamped together with a screw and nutcombination 58 and 59, but it should be understood that other mechanicalattachment means, such as a rivet, can also be used. The clampingsurfaces of both the shim and the insert mate with the joining angle ofthe V-spring and sit flush on that portion of the V-spring, so as toprevent play in the assembly during operation. The actual area ofcontact between the insert, the V-spring and the shim must be smallenough, however, to not significantly affect the overall stiffness ofthe V-spring member, but still great enough to provide an adequateclamping surface that the assembly lasts for the desired life of theproduct.

The insert and the shim portions of the node assembly should comprise abearing-type material with a low friction, less than that of theV-spring, which is typically made from steel, in order to avoid wearbetween the V-spring, the insert and the shim, and to maintain a gradualstress introduction zone in the V-spring. Furthermore, the material musthave a high enough yield strength to strongly hold the attachment member(rivet or screw), and yet must resist wear and loosening of the jointover the life of the product. Brass and bronze have shown to fulfillthese requirements. Both have good bearing properties and high yieldstrength. Other materials, such as aluminum and zinc, could also beused.

The entire node assembly must be clamped tightly to maintain a tightjoint therebetween, without play or movement between them, for thedesired life of the product. The overall geometry of the insert and theshim minimize the clamping pressure produced by the approximately 500 Nclamping force required to produce the desired tight arrangement, whilethe particular material of the insert and the shim creates a goodfriction/high wear tolerance surface between the V-spring, shim andinsert elements.

A variation of the second embodiment includes different insert and shimconfigurations, shown in FIGS. 7A, 7B and 8A, 8B, which provide therequired clamping surfaces for attachment and alignment of the V-springmember, with different insert and shim configurations, which alsoprovide a low friction bearing surface between the V-spring and the nodespring (mounting plate).

Referring now to FIG. 7, insert 98 is round in general configuration andincludes opposing flat side shoulder surfaces 104 and 105, which providethe required clamping surfaces between insert 98 and the V-spring 100,and positions the insert correctly relative to the V-spring. Again, theouter edges 106 of the flat side shoulder surfaces are rounded to avoidstress concentrations. The insert 98 also includes an upper raisedportion 108 which functions as a keying element, extending upwardthrough an opening in the V-spring. Upper surface portions 107 of theinsert have a slightly larger radius than the lower surface of theV-spring member and the joint thereof, so that the V-spring will sitflush on the flat shoulder portions of the insert when the assembly isclamped together.

Intermediate between the keying portion 108 and the flat shouldersurfaces 104, 105 is a bearing boss 109 which provides a bearing surfacefor the node opening in the V-spring. The height of the bearing boss 109must not interfere with the clamping action for the assembly, but isdesigned for an interference fit with an opening in the V-spring.

A groove 116 between the bearing boss 109 and the flat shoulder surfaces104, 105 of the insert allows the V-spring to sit flush on those flatshoulder portions. The keying element 108 is configured to provide aslight interference fit with the corresponding opening in the V-spring.Opening 110 through element 108 is adapted to receive an attachmentmember therethrough. The base surface 111 of insert 108 provides supportfor a nut in the case of a screw and nut assembly or a clamping surfacefor the deformed end of a rivet connector.

A flat shim portion 118 is circular, with a diameter of approximately 4mm, approximately 0.5 mm thick, with a central opening 112 which matchesthe raised keying portion 108 of the insert. The flat shim supports themounting plate 121, as shown in FIG. 7. An attachment member 120 securesthe existing assembly together firmly.

The above two variations can be in turn varied. For instance, thebearing boss portion of the insert of FIG. 8A can be used with theinsert of FIG. 4 for an interference fit with an opening in theV-spring.

In a further variation, the arrangement of FIGS. 7, 8A, 8B can bemodified so that the shim of FIG. 8B is replaced with the shim of FIGS.6A, 6B; and still further, the insert of FIG. 8A can be modified toeliminate the bearing boss and then used with the shim of FIGS. 6A, 6B.

Still further, the insert of FIG. 5 can be used with the shim of FIG.8B, and in yet another variation, the insert of FIG. 5 can be modifiedto include a bearing boss portion and used with the shim of FIG. 8B.

Hence, a nodal spring arrangement has been described in which a V-shapedtorsion member (spring) is secured at its node point to the handlehousing by a mounting plate. In one embodiment, the mounting plate iswelded to the V-shaped spring at the node point; slots provided in theV-shaped spring are located on opposing sides of the node point. Theseslots create a torsion bar node spring while also reducing stressesaround the node point connection zone. Another embodiment includes anode point assembly which includes an insert supporting the V-shapedtorsion spring and a shim member located between the V-shaped torsionspring and the mounting plate node spring, the assembly being heldtightly together by an attachment member combination, such as a screw ora rivet.

Although a preferred embodiment of the invention has been disclosed forpurposes of illustration, it should be understood that various changes,modifications and substitutions may be incorporated in the embodimentwithout departing from the spirit of the invention which is defined bythe claims which follow.

1-20. (canceled)
 21. A V-spring member for use in a driving system for apersonal care appliance, comprising: an elongated solid spring member(50), having a cross-sectional configuration in the form of a V, whereinthe spring member has regions (501, 502) at the ends thereof which arelarge enough to support a contact from an end clamping assembly, thespring member further including a cross-piece (504) extending betweenthe longitudinal edges of the spring member in the end regions thereof,such that the ends of the spring member define a closed loop.
 22. TheV-spring of claim 1, wherein the end regions extend a distance below thelongitudinal edges of the V-spring at each end of the V-spring.
 23. TheV-spring of claim 1, wherein the V-spring is made of steel.
 24. TheV-spring of claim 1, including openings in the vicinity of the ends ofthe V-spring to permit a bolt to extend therethrough for clamping of theends of the V-spring.
 25. The V-spring of claim 1, wherein the personalcare appliance is a toothbrush.